Halogen-free flame-retardant polyester resin for powder coating and preparation method thereof

Abstract

This invention relates to a halogen-free flame-retardant polyester resin for powder coatings. This polyester resin is obtained through a polymerization reaction using raw materials including piperazine, dimethyl adipate, p-phenylenediamine, melamine, succinic anhydride, diethylene glycol, 2-nitroterephthalic acid, adipic acid, and ammonium polyphosphate. The resulting polyester resin exhibits high branching, high rigidity, and extremely high nitrogen content in its molecular chain segments. The cured film exhibits high hardness and, without the presence of environmentally unfriendly halogen atoms, achieves an oxygen index exceeding 31%, demonstrating excellent flame-retardant properties. Furthermore, the polyester resin has low steric hindrance of its terminal carboxyl groups and high reactivity, allowing for low-temperature curing. The conventional properties of the coating film meet the application requirements of 60 / 40 powder coatings.

Description

Technical Field

[0001] This invention relates to the field of powder coating technology, specifically to a halogen-free flame-retardant polyester resin for powder coatings, its preparation method, and its application in 60 / 40 powder coatings. Background Technology

[0002] Powder coatings are increasingly used due to their advantages such as solvent-free evaporation and recyclability. Traditional powder coatings generally lack flame-retardant properties, and a large portion of decorative powder coatings are used indoors. While maintaining their aesthetic appeal, these coatings are flammable and pose significant safety hazards. Although some flame-retardant products have emerged in recent years, such as those disclosed in CN201610068148.8, CN201810327148.4, and CN202110828226.0, these powder coatings use elements like bromine and chlorine as flame-retardant components, failing to meet national environmental protection requirements for halogen-free flame retardants. This is because many fires have revealed that halogen atoms release large amounts of toxic substances during combustion, leading to injuries and fatalities. Currently, among indoor decorative coatings, 60 / 40 type powder coatings are widely used due to their relatively low cost and higher polyester resin content. However, since additive flame retardants do not have mechanical properties themselves, excessive addition can easily lead to a decrease in the mechanical properties of the coating film, resulting in insufficient performance such as easy powdering and boiling in water, and unsatisfactory impact resistance. How to develop halogen-free flame-retardant indoor 60 / 40 polyester resin that meets national environmental protection requirements is a problem that has been troubling the industry.

[0003] To address the aforementioned problems, this invention discloses a halogen-free flame-retardant polyester resin for powder coatings and its preparation method. This polyester resin is obtained through polymerization using raw materials including piperazine, dimethyl adipate, p-phenylenediamine, melamine, succinic anhydride, diethylene glycol, 2-nitroterephthalic acid, adipic acid, and ammonium polyphosphate. The resulting polyester resin exhibits high branching, high rigidity, and extremely high nitrogen content in its molecular chain segments, resulting in high coating hardness after curing. Furthermore, without the presence of environmentally unfriendly halogen atoms, its oxygen index can reach over 31%, demonstrating excellent flame-retardant properties. Moreover, the polyester resin has low steric hindrance of its terminal carboxyl groups and high activity, allowing for low-temperature curing (e.g., 165℃ / 15min) to form a film. The conventional properties of the coating film meet the application requirements of 60 / 40 powder coatings. Summary of the Invention

[0004] This invention relates to a halogen-free flame-retardant polyester resin for powder coatings, which is obtained by polymerization reaction using raw materials including piperazine, dimethyl adipate, p-phenylenediamine, melamine, succinic anhydride, diethylene glycol, 2-nitroterephthalic acid, adipic acid, and ammonium polyphosphate.

[0005] A halogen-free flame-retardant polyester resin for powder coatings comprises the following raw materials in molar amounts:

[0006]

[0007] The flame retardant ammonium polyphosphate is added at a rate of 2-3% of the piperazine mass;

[0008] The raw materials also include catalyst 1, catalyst 2, and antioxidant.

[0009] Among them, catalyst 1 is anhydrous potassium carbonate, and the amount used is 0.3-0.5% of the piperazine mass; catalyst 2 is monobutyltin oxide, and the amount used is 0.03-0.07% of the total raw material mass; the molar ratio of succinic anhydride to melamine is 3.2-3.4:1; antioxidant is antioxidant 1010, namely pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the amount used is 0.1-0.3% of the total raw material mass.

[0010] The preparation method of the halogen-free flame-retardant powder coating polyester resin includes the following steps:

[0011] A. Add the prescribed amounts of N,N-dimethylformamide and melamine to reactor 1, start stirring and heat to 110-120℃ to fully disperse and dissolve them, then add the prescribed amounts of succinic anhydride in batches. After all the succinic anhydride has been added, keep the reaction at 110-120℃.

[0012] B. Take samples to test the amine value of the system. When the amine value is lower than 5 mg KOH / g, cool the material solution to room temperature to obtain the melamine graft intermediate for later use.

[0013] C. Add the formulated amount of piperazine, p-phenylenediamine, dimethyl adipate and catalyst 1 to reaction vessel 2, and heat to 140-145℃ to carry out a heat-preserving ammonolysis polymerization reaction.

[0014] D. Take samples to test the content of piperazine. When the conversion rate of piperazine is >95%, add the prescribed amount of diethylene glycol and catalyst 2 to reaction vessel 2, heat to 150-155℃ to carry out transesterification reaction. After no obvious methanol is distilled off, add the prescribed amount of 2-nitroterephthalic acid to carry out polymerization reaction, gradually heat to 170-180℃, and keep the reaction at the temperature.

[0015] E. Sampling and testing: When the acid value of the polymer reaches 15-22 mg KOH / g, the melamine graft intermediate solution in reactor 1 is pumped to reactor 2, and the temperature is gradually raised to 220-225℃. Then, the chain extension polymerization reaction is carried out while maintaining the temperature. During the heating process, N,N-dimethylformamide solvent is removed.

[0016] F. When the acid value of the polymer reaches 29-36 mgKOH / g, add the prescribed amount of antioxidant and start the vacuum system for vacuum polycondensation.

[0017] G. When the acid value of the polymer reaches 15-20 mg KOH / g, stop the vacuum, add the prescribed amount of end-capping agent adipic acid to carry out the end-capping reaction, and stop the reaction when the acid value reaches 48-56 mg KOH / g. Cool down to 180-190℃, add the prescribed amount of ammonium polyphosphate, stir thoroughly, and discharge the material while it is still hot. Cool the polyester resin, and then crush and granulate it to obtain the flame-retardant polyester resin.

[0018] In step A, the succinic anhydride of the formula is added in four portions, with an interval of 10-15 minutes between each addition.

[0019] In step D, the temperature is increased to 170-180℃ at a heating rate of 10-12℃ / h; in step E, the temperature is gradually increased to 220-225℃ at a heating rate of 6-9℃ / h; in step F, the vacuum degree is controlled between -0.096Mpa and -0.098Mpa; in step G, the polyester resin is cooled with a steel belt containing cooling water.

[0020] For example, the method for using polyester resin in halogen-free flame-retardant powder coatings includes the following steps:

[0021] A. Add the prescribed amounts of N,N-dimethylformamide and melamine to reaction vessel 1, start stirring and heat to 110-120℃ to fully disperse and dissolve them. Then add the prescribed amounts of succinic anhydride in four portions, with an interval of 10-15 minutes between each addition. After all the succinic anhydride has been added, keep the temperature at 110-120℃ for the reaction.

[0022] B. Take samples to test the amine value of the system. When the amine value is lower than 5 mg KOH / g, it indicates that the melamine has basically completed the grafting reaction with succinic anhydride. Cool the material solution to room temperature to obtain the melamine grafting intermediate for later use.

[0023] C. Add the formulated amount of piperazine, p-phenylenediamine, dimethyl adipate and catalyst 1 to reaction vessel 2, and heat to 140-145℃ to carry out a heat-preserving ammonolysis polymerization reaction.

[0024] D. Take samples to test the content of piperazine. When the conversion rate of piperazine is >95%, it indicates that the polymerization reaction is basically completed. At this time, add the prescribed amount of diethylene glycol and catalyst 2 to reactor 2, and heat to 150-155℃ to carry out the transesterification reaction. After no obvious methanol is distilled out, it indicates that the dimethyl adipate end-capped part has been completely transesterified by diethylene glycol. At this time, add the prescribed amount of 2-nitroterephthalic acid to carry out the polymerization reaction, and raise the temperature to 170-180℃ at a heating rate of 10-12℃ / h, and keep the temperature for the reaction.

[0025] E. Sampling and testing: When the acid value of the polymer reaches 15-22 mg KOH / g, the melamine graft intermediate solution in reactor 1 is pumped to reactor 2. At the same time, the temperature is gradually increased to 220-225℃ at a heating rate of 6-9℃ / h. Then, the chain extension polymerization reaction is carried out by holding the temperature. During the heating process, N,N-dimethylformamide solvent is removed.

[0026] F. When the acid value of the polymer reaches 29-36 mgKOH / g, add the prescribed amount of antioxidant 1010, start the vacuum system for vacuum polycondensation, and control the vacuum degree at -0.096 MPa to -0.098 MPa.

[0027] G. When the acid value of the polymer reaches 15-20 mg KOH / g, stop the vacuum, add the prescribed amount of adipic acid as the end-capping agent to carry out the end-capping reaction. When the acid value reaches 48-56 mg KOH / g, stop the reaction, cool down to 180-190℃, add the prescribed amount of ammonium polyphosphate, stir thoroughly, discharge the material while it is hot, and cool the polyester resin with a steel belt with cooling water. Then crush and granulate to obtain flame-retardant polyester resin.

[0028] The resulting product is a light yellow transparent granule with an acid value of 48-56 mgKOH / g and a softening point of 108-119℃.

[0029] The present invention also relates to the application of the halogen-free flame-retardant powder coating polyester resin as described above or the halogen-free flame-retardant powder coating polyester resin obtained by the preparation method described above in 60 / 40 powder coatings.

[0030] For example, the 60 / 40 decorative powder coating formulation includes: polyester resin, E-12 epoxy resin, leveling agent, gloss enhancer, benzoin, etc.; the coating preparation method is as follows: mix the materials according to the powder coating formulation, extrude, press, and crush them separately using a twin-screw extruder, and then crush and sieve the sheet to make powder coating; the powder coating is sprayed onto the surface-treated aluminum alloy substrate with an electrostatic spray gun, with a film thickness of 100μm, and cured at 165℃ / 18min to obtain the coating.

[0031] Beneficial effects:

[0032] The polyester resin described in this invention is obtained through a polymerization reaction using raw materials including piperazine, dimethyl adipate, p-phenylenediamine, melamine, succinic anhydride, diethylene glycol, 2-nitroterephthalic acid, adipic acid, and ammonium polyphosphate. The resulting polyester resin exhibits high branching, high rigidity, and extremely high nitrogen content in its molecular chain segments. The cured film exhibits high hardness and, without the presence of environmentally unfriendly halogen atoms, achieves an oxygen index exceeding 31%, demonstrating excellent flame retardant properties. Other conventional properties also meet the application requirements for indoor 60 / 40 powder coatings. Furthermore, the polyester resin has low steric hindrance of its terminal carboxyl groups and high reactivity, allowing for low-temperature curing (165℃ / 15min) to form a film, with the conventional properties of the coating meeting the application requirements of 60 / 40 powder coatings. Detailed Implementation

[0033] The present invention will be further described below with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and technical features described in this application can be combined with each other. It should also be pointed out that, unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terms "comprising" or "including" and similar words used in this invention refer to elements or objects preceding the word that encompass the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0034] All raw materials described in this invention are commercially available.

[0035] Preparation Example 1

[0036] A halogen-free flame-retardant polyester resin for powder coatings comprises raw materials with the following molar composition:

[0037]

[0038] The flame retardant ammonium polyphosphate is added at 3% of the mass of piperazine.

[0039] Catalyst 1 is anhydrous potassium carbonate, and its dosage is 0.5% of the mass of piperazine; Catalyst 2 is monobutyltin oxide, and its dosage is 0.07% of the total mass of raw materials; Antioxidant is Antioxidant 1010, and its dosage is 0.3% of the total mass of raw materials.

[0040] The method for using polyester resin in halogen-free flame-retardant powder coatings includes the following steps:

[0041] A. Add the prescribed amount of N,N-dimethylformamide and melamine to reaction vessel 1, start stirring and heat to 120℃ to fully disperse and dissolve them, then add the prescribed amount of succinic anhydride in four portions, with an interval of 15 minutes between each addition. After all the succinic anhydride has been added, keep the reaction at 120℃.

[0042] B. Take samples to test the amine value of the system. When the amine value is lower than 5 mg KOH / g, it indicates that the melamine has basically completed the grafting reaction with succinic anhydride. Cool the material solution to room temperature to obtain the melamine grafting intermediate for later use.

[0043] C. Add the formulated amount of piperazine, p-phenylenediamine, dimethyl adipate and catalyst 1 to reaction vessel 2, and heat to 145℃ to carry out a heat-preserving ammonolysis polymerization reaction.

[0044] D. Take samples to test the content of piperazine. When the conversion rate of piperazine is >95%, it indicates that the polymerization reaction is basically completed. At this time, add the prescribed amount of diethylene glycol and catalyst 2 to reactor 2, and raise the temperature to 155℃ to carry out the transesterification reaction. After no obvious methanol is distilled out, it indicates that the dimethyl adipate end-capped part has been completely transesterified by diethylene glycol. At this time, add the prescribed amount of 2-nitroterephthalic acid to carry out the polymerization reaction, and raise the temperature to 180℃ at a rate of 12℃ / h, and keep the reaction at this temperature.

[0045] E. Sampling and testing: When the acid value of the polymer reaches 15-22 mgKOH / g, the melamine graft intermediate solution in reactor 1 is pumped to reactor 2. At the same time, the temperature is gradually increased to 225°C at a heating rate of 9°C / h. Then, the chain extension polymerization reaction is carried out by holding the temperature. During the heating process, N,N-dimethylformamide solvent is removed.

[0046] F. When the acid value of the polymer reaches 29-36 mg KOH / g, add the prescribed amount of antioxidant, start the vacuum system to carry out vacuum polycondensation, and control the vacuum degree at -0.098 MPa.

[0047] G. When the acid value of the polymer reaches 15-20 mg KOH / g, stop the vacuum, add the prescribed amount of end-capping agent adipic acid to carry out the end-capping reaction, stop the reaction when the acid value reaches the expected value, cool down to 190℃, add the prescribed amount of ammonium polyphosphate, stir thoroughly, discharge the material while it is hot, and cool the polyester resin with a steel belt with cooling water, then crush and granulate to obtain flame-retardant polyester resin.

[0048] The resulting product is a light yellow transparent granule with an acid value of 53 mg KOH / g and a softening point of 112℃.

[0049] Preparation Example 2

[0050] A halogen-free flame-retardant polyester resin for powder coatings comprises raw materials with the following molar composition:

[0051]

[0052]

[0053] The flame retardant ammonium polyphosphate is added at a rate of 2% of the piperazine mass.

[0054] Catalyst 1 is anhydrous potassium carbonate, used at 0.4% of the mass of piperazine; Catalyst 2 is monobutyltin oxide, used at 0.05% of the total mass of raw materials; Antioxidant is Antioxidant 1010, used at 0.3% of the total mass of raw materials.

[0055] The preparation method is the same as in Preparation Example 1.

[0056] The resulting product is a light yellow transparent granule with an acid value of 50 mg KOH / g and a softening point of 117℃.

[0057] Preparation Example 3

[0058] A halogen-free flame-retardant polyester resin for powder coatings comprises raw materials with the following molar composition:

[0059]

[0060] The flame retardant ammonium polyphosphate is added at 3% of the mass of piperazine.

[0061] Catalyst 1 is anhydrous potassium carbonate, used at 0.5% of the mass of piperazine; catalyst 2 is monobutyltin oxide, used at 0.07% of the total mass of raw materials; antioxidant is antioxidant 1010, used at 0.2% of the total mass of raw materials.

[0062] The preparation method is the same as in Preparation Example 1.

[0063] The resulting product is a light yellow transparent granule with an acid value of 52 mg KOH / g and a softening point of 114℃.

[0064] Preparation Example 4

[0065] A halogen-free flame-retardant polyester resin for powder coatings comprises raw materials with the following molar composition:

[0066]

[0067] The flame retardant ammonium polyphosphate is added at 3% of the mass of piperazine.

[0068] Catalyst 1 is anhydrous potassium carbonate, used at 0.5% of the mass of piperazine; catalyst 2 is monobutyltin oxide, used at 0.07% of the total mass of raw materials; antioxidant is antioxidant 1010, used at 0.2% of the total mass of raw materials.

[0069] The preparation method is the same as in Preparation Example 1.

[0070] The resulting product is a light yellow transparent granule with an acid value of 49 mg KOH / g and a softening point of 116℃.

[0071] Comparative preparation example 1:

[0072] The powder coating was made from commercially available 60 / 40 polyester resin, model SJ6018, manufactured by Anhui Shenjian New Material Co., Ltd., and cured at 180℃ for 15 minutes.

[0073] Examples 1-4, Comparative Example 1 (polyester resins were obtained from Preparation Examples 1-4 and Comparative Preparation Example 1, respectively):

[0074] 60 / 40 decorative powder coating formulation (parts by weight): 360 parts of the above-mentioned polyester resin, 240 parts of E-12 epoxy resin, 8 parts of leveling agent, 8 parts of gloss enhancer, and 3 parts of benzoin.

[0075] Coating preparation: All materials are mixed according to the above powder coating formula, and then extruded, pressed, and crushed separately using a twin-screw extruder. The sheets are then pulverized and sieved to produce the powder coating. The powder coating is applied to the surface-treated aluminum alloy substrate using an electrostatic spray gun, with a film thickness of 100 μm. After curing at 165℃ for 18 min, the coating is obtained.

[0076] Coating performance testing was conducted according to GB / T 21776-2008 "Guideline for Testing Standards of Powder Coatings and Their Coatings"; film hardness testing was performed according to GB / T 6739-2006 "Determination of Hardness of Paint Films by Pencil Method for Paints and Varnishes". For the flame retardant properties of the coating, the coating was cut and scraped off with a knife, and then tested according to GB / T2406-93 "Test Method for Combustion Performance of Materials - Oxygen Index Method".

[0077] The polyester resins prepared in Preparation Examples 1-4 and Comparative Preparation Example 1 were used to prepare coatings according to the coating formulation provided by the present invention. The coating performance results are shown in Table 1 below.

[0078] Table 1 Powder Coating Film Performance

[0079] sample Coating appearance Gloss (60° angle) Impact performance (50cm) Coating hardness Oxygen index (%) Boil in boiling water for 2 hours. Example 1 Smooth 93.5 Both positive and negative impacts passed 2H 31.6 No change Example 2 Smooth 93.2 Both positive and negative impacts passed 3H 32.4 No change Example 3 Smooth 93.9 Both positive and negative impacts passed 2H 33.1 No significant changes Example 4 Smooth 94.1 Both positive and negative impacts passed 2H 32.2 No change Comparative Example 1 Smooth 93.7 Both positive and negative impacts passed H 20.5 No significant changes

[0080] As can be seen from the table above, the 60 / 40 powder coating prepared by the present invention has better appearance and impact performance after low-temperature curing (165℃ / 18min). Its gloss and boiling water properties are basically equivalent to those of commercially available 60 / 40 polyester resin powder coating under conventional curing conditions (180℃ / 15min). However, the product obtained through special monomer and process design has significantly improved coating hardness, with the coating hardness generally above 2H, which is significantly higher than that of the coating hardness of Comparative Example 1. In particular, without the use of traditional halogen atoms, the oxygen index of its coating is above 31%, which is much higher than that of commercially available products.

[0081] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above description is illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A halogen-free flame-retardant polyester resin for powder coatings, characterized in that, Including the following raw materials in molar amounts: Piperazine 20-30 parts; 3-5 parts of p-phenylenediamine; 28-40 parts of dimethyl adipic acid; 5-7 parts of melamine; 17-23 parts of succinic anhydride; 20-30 parts of diethylene glycol; 7-11 parts of 2-nitroterephthalic acid; 4-6 parts adipic acid; 30-40 parts of N,N-dimethylformamide; Ammonium polyphosphate flame retardant, added at a rate of 2-3% of piperazine mass; The raw materials also include catalyst 1, catalyst 2 and antioxidant; catalyst 1 is anhydrous potassium carbonate, and the amount used is 0.3-0.5% of the mass of piperazine; catalyst 2 is monobutyltin oxide, and the amount used is 0.03-0.07% of the total mass of the raw materials.

2. The polyester resin for halogen-free flame-retardant powder coating as described in claim 1, further characterized in that the molar ratio of succinic anhydride to melamine is 3.2-3.4:

1.

3. The halogen-free flame-retardant powder coating polyester resin as described in claim 1, further characterized in that the antioxidant is antioxidant 1010, and the amount used is 0.1-0.3% of the total mass of the raw materials.

4. A method for preparing a halogen-free flame-retardant powder coating polyester resin according to any one of claims 1-3, characterized in that, Includes the following steps: A. Add the prescribed amounts of N,N-dimethylformamide and melamine to reactor 1, start stirring and heat to 110-120℃ to fully disperse and dissolve them, then add the prescribed amounts of succinic anhydride in batches. After all the succinic anhydride has been added, keep the reaction at 110-120℃. B. Take samples to test the amine value of the system. When the amine value is lower than 5 mg KOH / g, cool the material solution to room temperature to obtain the melamine graft intermediate for later use. C. Add the formulated amount of piperazine, p-phenylenediamine, dimethyl adipate and anhydrous potassium carbonate catalyst 1 to reactor 2, and heat to 140-145℃ to carry out a heat-preserving ammonolysis polymerization reaction. D. Take samples to test the content of piperazine. When the conversion rate of piperazine is >95%, add the prescribed amount of diethylene glycol and catalyst 2 monobutyltin oxide to reactor 2, heat to 150-155℃ to carry out transesterification reaction. After no obvious methanol is distilled off, add the prescribed amount of 2-nitroterephthalic acid to carry out polymerization reaction, gradually heat to 170-180℃, and keep the reaction at the temperature. E. Sampling and testing: When the acid value of the polymer reaches 15-22 mgKOH / g, the melamine graft intermediate solution in reactor 1 is pumped to reactor 2, and the temperature is gradually raised to 220-225℃. Then, the chain extension polymerization reaction is carried out while maintaining the temperature. During the heating process, N,N-dimethylformamide solvent is removed. F. When the acid value of the polymer reaches 29-36 mgKOH / g, add the prescribed amount of antioxidant and start the vacuum system for vacuum polycondensation. G. When the acid value of the polymer reaches 15-20 mg KOH / g, stop the vacuum, add the prescribed amount of end-capping agent adipic acid to carry out the end-capping reaction, and stop the reaction when the acid value reaches 48-56 mg KOH / g. Cool down to 180-190℃, add the prescribed amount of ammonium polyphosphate, stir thoroughly, and discharge the material while it is still hot. Cool the polyester resin, and then crush and granulate it to obtain the flame-retardant polyester resin.

5. The method for preparing halogen-free flame-retardant powder coating polyester resin as described in claim 4 is further characterized in that, in step A, the formulated amount of succinic anhydride is added in four portions, with an interval of 10-15 minutes between each addition.

6. The method for preparing halogen-free flame-retardant powder coating polyester resin as described in claim 4 is further characterized in that, in step D, the temperature is raised to 170-180°C at a heating rate of 10-12°C / h; and in step E, the temperature is gradually raised to 220-225°C at a heating rate of 6-9°C / h.

7. The method for preparing halogen-free flame-retardant powder coating polyester resin as described in claim 4, further characterized in that, in step F, the vacuum degree is controlled at -0.096 MPa to -0.098 MPa; and in step G, the polyester resin is cooled with a steel belt containing cooling water.

8. The application of the halogen-free flame-retardant polyester resin for powder coatings as described in claims 1-3 or the halogen-free flame-retardant polyester resin for powder coatings prepared by the method described in claims 4-7 in 60 / 40 powder coatings.

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